Locating a target through media

ABSTRACT

A printer is disclosed. The printer uses a target located on one side of media to position an image on the other side of the media. The printer backlights the media and uses a sensor that locates the target through the backlit media.

BACKGROUND

Some signs or billboards are designed to be viewed both during the dayand during the night. During the day the illumination for the sign istypically daylight reflecting off the front surface of the sign. Atnight the signs are illuminated with a light source. Some signs areilluminated with a light source that mimics daylight by directing lighttowards the front surface of the sign. Other signs are backlit with alight source that is behind the sign that directs light through thesign.

Backlit signs may have an image printed on the front side of the signand a mirrored copy of the image printed on the back side of the sign.When viewed during the day the front image is seen. When viewed at nightthe final image seen is a combination of the image printed on the backside of the sign and the image printed on the front side of the sign.The image printed on the back side of the sign may be less saturatedthan the image printed on the front side. By printing a less saturatedcopy of the image on the back side the combined image seen at night canbe color matched to the front side image when viewed during the day.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of an example printer 100.

FIG. 2 is a sectional top view of the example printer 100.

FIG. 3 is a sectional top view of another example printer.

FIG. 4A is an example of the printing on side A.

FIG. 4B is an example target being scanned.

FIG. 4C is an example target being scanned,

FIG. 4D is an example target being scanned,

FIG. 5 is an electrical block diagram of an example printer 500.

FIG. 6 is an example block diagram of the processor coupled to memory564.

FIG. 7 is an example flow chart for a method of printing.

DETAILED DESCRIPTION

Signs or billboards that are used both during the day and at night areknown as “day and night” signs or “D&N” signs. When printing on mediafor a D&N sign, the same image is printed on the front side and the backside of the media with the back image a mirrored copy of the front sideimage. When the image printed on the front side is not aligned with theimage printed on the back side the combined image viewed at night mayhave quality issues, for example it may have blurred edges or othervisual defects.

Aligning the two images may be difficult. Currently the two images aremanually aligned. A mark or target is printed along with the image onone side of the media. The position of the mark is measured in the X andY direction with respect to a feature on the media, for example an edge.The measured distances are input as an offsets when printing the imageon the second side of the media. This method has a number of problems.One problem is that the measurements are typically done by hand and areprone to errors. Another problem is that the edges of the media may notbe aligned to the printer in the same way after the media has beenflipped over when printing on the second side. Another reason thatcreates difficulty is that the media used for D&N printing is typicallybetween 50% and 95% opaque, for example 90% opaque.

In one example a printer will print an image of one or more targets onthe first side of the D&N media. The media will be flipped over and amirrored copy of the first image will be printed on the second side ofthe media. The mirrored copy of the image printed on the second sidewill be aligned to the image on the first side using the targets printedon the first side. The printer will locate the targets using a sensorthat looks through the media to locate the targets on the first sidewhen the second side is being printed. The sensor will be able to locatethe targets through the media because a media path runs between thesensor and a light source. Because the media is between the light sourceand the sensor the light source backlights the media allowing the sensorto locate the targets. Once the second side has been printed the targetsare typically trimmed off, leaving only the images printed on both sidesof the media.

FIG. 1 is a side view of an example printer 100. Printer 100 comprises amedia source 102, a pair of pinch rollers 104, a pair of take-up rollers106, a print engine 108, a sensor 110, a light source 112 and media 114.A media path runs from the media source 102, between the pair of pinchrollers 104, underneath the print engine 108 and between the pair oftake-up rollers 106. Media 114 is shown in the media path. Duringprinting the media 114 travels along its length in a printing directionas shown by arrow 122. A print zone 116 is underneath the print engine108. The print zone is defined as the location where printing fluid fromthe print engine is deposited onto the media 114. Printing fluid is anyliquid that is deposited by the print engine and can comprise black ink,colored inks, gloss, pre-treatment fluids, finishing fluids and thelike.

In this example, sensor 110 is located on the print engine 110. In otherexamples the sensor may be located in a different position, for exampleadjacent to the print engine. Sensor 110 can be any type of sensor thatdetects light intensity, for example a charged coupled device (COD).Media 114 has a first side 118 and a second side 120. The first side 118of the media is facing the print engine 108. Sensor is located above thefirst side 118 of the media 114.

Light source 112 is located below the sensor 110 facing the second side120 of the media 114 such that the media path travels between the sensor110 and the light source 112. Light 119 from the light source isdirected towards the sensor. Light 119 from the light source 112 travelsthrough the media 114 towards the sensor 110. Because the light travelsthrough the media 114 the light 119 backlights the media such that thesensor can detect images and/or targets printed on the second side 120of the media.

In one example, media 114 is “day and night” (D&N) media. D&N media mayalso be known as banner media. D&N media is typically between 50% and95% opaque, for example 90% opaque. D&N media typically comes in a rollor web containing 50 meters or more of material, but may also come assheets of media. D&N media is typically fabricated from PVC, but may befabricated from other materials. D&N media may typically be between 0.5mm and 2.0 mm thick, for example 1.0 mm thick.

FIG. 2 is a sectional top view of the example printer 100. In thisexample print engine 108 is configured as a carriage mounted on guiderail 232. The carriage travels back and forth across the width W of themedia 114 as shown by arrow 234. In some examples the width of the mediamay be between 60 and 180 inches wide (1524 to 4572 mm wide), forexample 130 inches (3,302 mm) wide. In other examples the width of themedia may be smaller or larger. The print engine 108 may also comprisemotors, drive belts or gears, additional guide rails, linear positionsensors and the like, but these items are not shown for clarity.

Printheads (230 A-D) mounted in the carriage deposit printing fluidsonto the first side 118 (see FIG. 1) of media 114 as the carriagetravels across the width of the media 114. In this example 4 printheads(230 A-D) are shown mounted in the carriage. Printheads (230 A-D) areremovably mounted in the print engine and are typically userloadable/replaceable. Each printhead may deposit a different printingfluid, for example the printheads (230 A-D) may deposit black ink, cyanink, yellow ink and magenta ink, respectively. In other examples theremay be more or fewer printheads mounted in the carriage. When printingan image the media 114 is advanced in the printing direction 122 aftereach swath of the image is printed.

Sensor 110 is mounted in the carriage and sweeps back and forth acrossthe media with the carriage. Light source 112 is positioned underneaththe path the sensor makes as it travels back and forth across the media.The media 114 travels between the sensor 110 and the light source 112thereby allowing the light source to backlight the media. In someexamples the sensor 110 can be used when the printheads are depositingprinting fluids onto the media 114 and when the carriage is sweepingacross the media when the printheads are not depositing printing fluidsonto the media 114. By sweeping the carriage across the full width ofthe media and incrementally advancing the media 114 in the printingdirection, the sensor can scan all areas of the media.

FIG. 3 is a sectional top view of another example printer. In thisexample print engine 108 is configured as a page wide array (PWA) ofprintheads. The printheads (330-338) are arranged in a staggered linethat stretches across the width of the media 114. In other examples asingle wide printhead may stretch across the full width of the media.When printing the print engine remains stationary as the media movesunderneath the print engine in the printing direction 122. In thisexample there are 5 printheads that are mounted in the print engine andstretch across the width of the media. In other examples there may bemore or fewer printheads. Each printhead may deposit multiple types ofprinting fluid as the media moves underneath the print engine. Forexample, each printhead may deposit black ink, cyan ink, yellow ink andmagenta ink. In other examples additional printing fluids may bedeposited by each printhead.

In the present example, sensor 110 is a line sensor, for example a lineof CODs that stretch across the width of the media 114. As the mediamoves in the printing direction 122 the sensor can scan the full widthof the media 114. Light source 112 is positioned underneath sensor 110.The media 114 travels between the sensor 110 and the light source 112thereby allowing the light source to backlight the media 114.

In operation, printer 100 prints an image and at least one target on oneside of the media and then prints a mirrored copy of the image on theother side of the media after the media is flipped over. In thisapplication the side of the media that gets printed on first will becalled side A. The side that gets printed on second, after the media ifflipped over, will be known as side B. In some examples, the media is ina continuous roll. The roll of media is flipped over after the image isprinted on side A such that the image can be printed on side B. In otherexamples, the media may start as sheets of media, or may be cut intosheets after printing on side A. After printing on side A, the sheets ofmedia would be flipped over such that the image can be printed onto sideB.

Printer 100 prints an image and one or more targets onto side A of themedia. The media is flipped over such that side B of the media is nowfacing the print engine. As the flipped media is advanced into the printzone the printer turns on the light source 112 backlighting the media.The sensor is used to scan and locate any targets on side A through themedia. A mirrored copy of the image printed on side A of the media isprinted onto side B of the media that is now facing the print engine.The mirrored copy of the image printed on side B is aligned to the imageprinted on the side A using the location of the targets printed on sideA of the media.

FIG. 4A is an example of the printing on side A. The printing on side Acomprises an image 440 and one or more targets 442 printed on both sidesof the image 440. In this example the targets 442 are printed in a rowdown both sides of the image 440. In other examples fewer targets may beused, for example only one target 442 printed on one side of the image440. In this example the targets are shaped like the letter ‘N’. Inother examples other shapes may be used. The position of the targetsrelative to the position of the image is known. Therefore when thelocation of a target is determined, the location of the image is known.

Scanning the target with a scan line creates peaks and valleys of lightdensity. The peaks and valleys depend on where the scan line intersectsthe target. FIG. 4B is an example target being scanned. Target 442 isshaped like the letter ‘N’. Scan line 550 is shown passing through themiddle of target 442 without any skew. Line 552 is a plot of the opticalintensity from scan line 550. The distance d1 is the distance betweenthe two outer peaks. When the scan line passes through the target withno skew distance d1 is equal to the actual width W of target 442.Distance d2 is the distance between the middle peak and one of the outerpeaks. In this example distance d2 is equal to ½ distance d1, indicatingthat scan line 550 is exactly between the top and bottom of target 442.

FIG. 4C is an example target being scanned. Scan line 550 is shownpassing through the top of target 442 without any skew. Line 552 is aplot of the optical intensity from scan line 550. The distance d1 is thedistance between the two outer peaks. When the scan line passes throughthe target with no skew distance d1 is equal to the actual width W oftarget 442. Distance d2 is the distance between the middle peak and oneof the outer peaks. In this example distance d2 is greater than ½distance d1, indicating that scan line 550 is near the top of target442.

FIG. 4D is an example target being scanned. Scan line 550 is shownpassing through the top of target 442 with some skew. Line 552 is a plotof the optical intensity from scan line 550. The distance d1 is thedistance between the two outer peaks. When the scan line passes throughthe target with skew, distance d1 is greater than the actual width W oftarget 442. The difference between distance d1 and the actual width Wcan be used to determine the amount of skew.

In one example the sensor will scan with a resolution of 600 samples perinch. In other examples the resolution may be higher or lower. When theprint engine is configured as a carriage (as shown in FIG. 2) thesampling rate for the sensor is dependent on the speed of the carriage.When the maximum carriage speed is 60 inches per second, the desiredresolution of 600 samples per inch results in a sampling rate for thesensor of 36 KHz. When the print engine is configured as a PWA, the linescanner will have a pixel spacing that matches the desired resolution.

FIG. 5 is an electrical block diagram of an example printer 500. Printercomprises a controller 562, memory 564, input/output (I/O) module 566,print engine 568, sensor 574 and a light source 576 all coupled togetheron bus 572. In some examples printer may also have a user interfacemodule, an input device, and the like, but these items are not shown forclarity. Controller 562 comprises at least one processor. The processormay comprise a central processing unit (CPU), a micro-processor, anapplication specific integrated circuit (ASIC), or a combination ofthese devices. Memory 564 may comprise volatile memory, non-volatilememory, and a storage device. Memory 564 is a non-transitory computerreadable medium. Examples of non-volatile memory include, but are notlimited to, electrically erasable programmable read only memory (EEPROM)and read only memory (ROM). Examples of volatile memory include, but arenot limited to, static random access memory (SRAM), and dynamic randomaccess memory (DRAM). Examples of storage devices include, but are notlimited to, hard disk drives, compact disc drives, digital versatiledisc drives, optical drives, and flash memory devices.

I/O module 566 is used to couple printer to other devices, for examplethe Internet or a computer. Printer has computer executable code,typically called firmware, stored in the memory 564. The firmware isstored as computer readable instructions in the non-transitory computerreadable medium (i.e. the memory 564) The processor generally retrievesand executes the instructions stored in the non-transitorycomputer-readable medium to operate the printer and to executefunctions. In one example, processor executes code that aligns andprints images onto a second side of media.

FIG. 6 is an example block diagram of the processor coupled to memory564. Memory 564 contains firmware 680. Firmware 680 contains analignment module 684. The processor executes the code in the alignmentmodule 684 to print an image on the second side of D&N media. Thealignment module may use the method shown in FIG. 7 to print an image onthe second side of D&N media.

FIG. 7 is an example flow chart for a method of printing. At 790 animage and at least one target is printed on side A of media. At 792 theposition of the at least one target is located using a sensor that looksthrough the media while the media is backlit. At 794 a mirrored copy ofthe image is printed on side B where the mirrored copy is positionedrelative to the at least one target on side A of the media.

What is claimed is:
 1. A printer comprising: a print engine; acontroller to control the print engine to form an image on a medium in aprint zone of a media path that extends through the printer and includesthe print zone; a sensor located on a first side of the media path; alight source located on a second side of the media path arranged todirect light to the sensor across the media path; the controller todetermine a location on a medium in the print zone of a printed targetthat is printed on a side of the medium that is adjacent to the lightsource, the controller determining the location on the medium of theprinted target based on output from the sensor which senses the printedtarget through the medium using light from the light source which haspassed through the medium.
 2. The printer of claim 1, the controller todetermine a location to print an image on a side of the medium adjacentthe print engine based on the location of the printed target identifiedon an opposite side of the medium using the sensor and light source. 3.The printer of claim 2, wherein, under control of the controller, theimage is a mirror image of a previous image already printed on theopposite side of the medium with the target.
 4. The printer of claim 3,the controller to determine locations for printed targets printed onboth sides of the previous image.
 5. The printer of claim 1, wherein theprint engine and sensor are disposed on a moveable carriage so as to bescanned across a width of the print zone transverse to the media path.6. The printer of claim 1, wherein the print engine comprises apage-width array of printheads and the sensor comprises a line sensor,and the sensor and light source both extend across a width of the printzone.
 7. The printer of claim 1, wherein, when the printed target isshaped as an “N,” the controller to track movement of an absorption peakcaused by the central slanted line of the “N” as movement of the mediumpasses the printed target between the sensor and light source.
 8. Theprinter of claim 1, the sensor to scan with a resolution of 600 samplesper inch of the medium.
 9. A method, comprising: back-lighting a mediumwith a light source disposed on a back side of the medium; sensing lightfrom the light source that has passed through the medium with a sensorlocated on a front side of the medium; advancing the medium along amedia path between the light source and sensor; and identifying alocation, on the back side of the medium, of a printed target printed onthe back side of the medium, wherein the location is identified based oninterference by the printed target of light from the light source asdetermined from output of the sensor.
 10. The method of claim 9, furthercomprising determining a location at which to print an image on thefront side of the medium based on the location of the printed target onthe back side of the medium.
 11. The method of claim 10, furthercomprising printing the image at the location on the front side of themedium that was determined based on the location of the printed targeton the back side of the medium.
 12. The method of claim 11, wherein theimage is a mirrored copy of a previous image already printed on the backside of the medium along with the printed target.
 13. The method ofclaim 12, further comprising printing the mirrored copy with a lowersaturation than the previous image.
 14. The method of claim 12, whereinthe printed target comprises shapes printed on both sides of theprevious image on the back side of the medium.
 15. The method of claim9, wherein the printed target comprises a mark that is shaped as an “N.”16. The method of claim 15, further comprising tracking movement of anabsorption peak caused by the central slanted line of the “N” asmovement of the medium passes the printed target between the sensor andlight source.
 17. The method of claim 15, wherein the printed targetcomprises a row of marks, each mark shaped as an “N,” disposed beforeand after the previous image along a direction the medium moves in themedia path.
 18. The method of claim 9, wherein the media is between 50%and 95% opaque.
 19. The method of claim 9, further comprising the sensordetecting light from the light source with a resolution of at least 600samples per inch of the medium.
 20. The method of claim 9, furthercomprising printing a day-and-night sign by: printing an image at alocation on the front side of the medium determined based on thelocation of the printed target on the back side of the medium, the imagebeing a mirrored copy of a previous image already printed on the backside of the medium along with the printed target; and removing a portionof the medium comprising the printed target.